1. Field of the Invention
The present invention relates to a battery device including a plurality of batteries connected in series, such as a battery package, and more particularly to a battery device that remains operative even if the battery heats up abnormally.
2. Description of the Related Art
With battery devices including a plurality of batteries connected in series, a technique is known which provides a thermally responsive switch for safety purposes in the event of abnormal heating of the batteries. More specifically, continuing to supply electricity to an overheating battery increases the chance of leakage. Therefore, thermally responsive switches are provided between the batteries connected in series and if the temperature inside the battery package increases to the point at which it is detected as abnormal, the thermally responsive switch is turned off to interrupt the supply of electricity to all the batteries.
The thermally responsive switch includes a thermally responsive element such as a bimetal strip which is composed of a plurality of laminated metal plates having different thermal expansion coefficients. This bimetal strip is fixed to a housing at one end thereof while the other end is free to move. The free end of the bimetal strip is provided with a movable contact which faces a fixed contact provided on the housing and can be in contact with the fixed contact. Below a predetermined temperature, the movable contact is in contact with the fixed contact, that is, the thermally responsive switch is on. If the temperature exceeds the predetermined temperature, the bimetal strip is inverted and the movable contact is detached from the fixed contact, thereby turning off the thermally responsive switch. Therefore, this type of thermally responsive switch is preferable for a thermal protector for detecting abnormal heating and eliminates or suppresses abnormal heating.
With such known battery devices described above, if the thermally responsive switch detects abnormal temperature elevation in one battery, the electricity supply to all the batteries is discontinued, thereby halting the power-supply function. More specifically, even though only one battery malfunctions and the other batteries operate normally, electrical equipment using the battery device as a power supply no longer functions. In this respect, this type of battery device is not efficient. Furthermore, even after electricity supply to the defective battery is interrupted, the temperature of the battery device does not immediately fall. Thus, a cooling fan or an alarm may be actuated for safety purposes, but with those known battery devices, the thermally responsive switch is not connected to an external circuit such as a protection circuit to output instruction signals. Hence, a safety mechanism for the abnormal heating of batteries could be complicated.